Nonnus the Mythographer's date is uncertain but he is said to have lived in Palestine in the middle of the sixth century AD, but more probably a century later.

Comentary on In Julianum Imperatorem invectivae duce of Gregory Nazianzen.

Mithras therefore the Persians consider to be the Sun, do sacrifice to him, and observe certain rites in his honour. No one can participate in his service without passing first through the grades of discipline. These grades are eighty in number, with descent and ascent, for the tests applied are first of an easier character, then more difficult; and thus after passing through all the grades the disciple arrives at perfection. The successive disciplinary tests are by fire, by cold, by hunger and thirst, by prolonged exertion, and in a word by similar trials of all kinds.

Comentary on In Julianum Imperatorem invectivae duce of Gregory Nazianzen.

Mithras is considered by the Persians to be the Sun. And to him they offer many sacrifices, and observe certain rites in his honour. No one can be initiated into the rites of Mithras without passing through all the disciplines and giving proof of self-control and chastity. Eighty grades are enumerated through which the postulant must pass in succession; for example, plunging first into deep water for many days, then throwing himself into fire, then solitary fasting in a desert place, and others also until as stated above has passed through the eighty. Then finally if he survives he receives the highest initiation, or if he has succumbed an (honourable) sepulchre.

Comentary on In Sancta lumina of Gregory Nazianzen

Different views are held with regard to Mithras. Some identify him with the Sun, others with the guardian of the fire, otehrs with a specific force, and certain rites are observed in his honour, especially among the Chaldeans. The aspirants to initiation pass through a series of disciplinary grades, undergoing first the easier forms of penance, then the more difficult. For example fasting is first imposed upon the neophytes for a period of about fifty days. If this is successfully endured, for two days they are exposed to extreme heat, then again plunged into snow for twenty days. And thus the severity of the discipline is gradually increased, and if the postulant shows himself capable of endurance he is finally admitted to the highest grades.

Cosmas of Jerusalem

Cosmas, known as Cosmas the younger, was a native of Jerusalem, and became bishop of Maiuma in Palestine in 743 AD.

The disciplinary grades of Mithra are reported to be eighty in number, through which the candidate for initiation must pass in succession. In addition to those already described there is immersion in water for many days, passing through fire, solitude and fasting in the wilderness, and numerous others until the end of the eighty disciplines is reached. And they do not allow participation in the rites of Mithras to anyone who has not passed through all the grades and approved himself pure and self-controlled.